This invention relates generally to the art of ultrafiltration, and in particular to a process of using ultrafiltration to separate valuable nutrients from cheese whey. It has been estimated that well in excess of twenty billion pounds of whey are produced in the United States each year as a by-product of the cheese industry. In manufacturing cheese, the curd is separated from the whey and the former is cured to produce cheese. The curd itself contains up to about ninety percent of the original milk protein, while the balance of such protein remains in the whey. The whey also contains substantial quantities of lactose, a comercially valuable sweetner used extensively by the baking industry.
Cheese factories are confronted with the problem of disposing of the whey, as no commercially practical methods have been developed for separating whey's valuable constituents, i.e., proteins and lactose, even though it has been known for years that an important source of protein and lactose is being wasted. A great amount of research time and money has been spent attempting to solve the problem. For example, see McDonough and Mattingly, "Pilot Plant Concentration of Cheese Whey by Reverse Osmosis," Food Technology, 24: 194,1970.
Some benefit has been derived from whey by merely concentrating the protein and lactose to provide an impure powder for animal and human consumption, but this procedure can be profitable only in times of rising meat prices. For the most part, then, the whey is dumped onto fields, in ditches, or into rivers and streams. However, due to the high BOD and COD of cheese whey, serious pollution problems result from dumping whey, and the USDA, FDA and Federal and State environmental agencies have launched an attack on the cheese industries for its whey disposal practices. Some cheese plants have been forced to close or pay large fines because of the whey pollution problems.
At the same time that literally millions of pounds of protein and lactose are being discarded with cheese whey, scientific researchers and nutritionists are searching for suitable milk replacers for infant formulas, high protein diet supplements and animal food enhancers. It is known that the proteins contained in cheese whey are highly desirable. Such proteins are literally "power-packed" in that they are rich in essential amino acids which cannot be found elsewhere in natural food products. In addition, the proteins are soluble in water and the resultant "milk" is quite palatable. The lactose material in whey is highly soluble, has fine browning characteristics in baked goods, and has considerable food and energy values. It is clear then that an economically feasible process for separating nutrients from cheese whey would benefit several major food processing industries in this country and throughout the world.
Some discussion of prior attempts at separating cheese whey proteins from other ingredients will be helpful. The earliest methods used chemical separation techniqes such as pH adjustment, heat treatments, flocculation, etc. to produce low yields of highly denatured proteins. The products from such processes do not possess the desired solubility and taste qualities required for milk replacers. Electrodialysis has also been employed to separate salts from cheese whey proteins, but this process is slow and expensive, mainly due to high power requirements.
The most recent efforts to separate protein from cheese whey have employed the principles of ultrafiltration or reverse osmosis. The osmosis process utilizes a semipermeable membrane flanked on either side by a concentrated solute solution and a less concentrated solution. Natural osmotic forces will tend to equalize the solute concentration by passing water through the membrane, while the solute cannot pass through the membrane. By applying a pressure to the concentrated solution, pure water can be forced back through the membrane, oppositely to the normal osmotic flow, thereby concentrating the solute. In ultrafiltration, on the other hand, pressure is applied to a solution to force the solvent through a semipermeable membrane.
Recent attempts at employing these processes for cheese whey separation have used a membrane which is selected so that protein will not pass through the membrane, but through which lactose and other constituents of whey will pass. Membranes have been designed in various shapes, including flat plates and hollow tubes. Tubular membranes are not particularly desirable because of the high rate of membrane clogging from whey solids leading to frequent repair or replacement of the costly membranes.